You have to think, how many times does 1296 go into 8409? It goes in 6 times, so just write that in the correct slot and continue the long division process. It may take a lot of estimating and huge multiplication, but it shouldn't be impossible.
When you figure out the fraction places after finding the base number that is correct, we must remember that every decimal place in the divisor takes out a decimal place in the dividend. So, the dividend's decimal place gets scooted over 2ce. Now, just line up the answer with the dividend's decimal place, and you have your answer!
If you have any other questions or want to follow up on this, feel free to contact me. Otherwise, I hope this helps you and your son! :)